Trace cisplatin and carboplatin removal by 3-mercaptopropionic acid and L-cysteine functionalized sponges: Adsorption behaviour and mechanism

This study presents functionalized open-celled cellulose Metalzorb® sponge (Sponge) with 3-mercaptopropionic acid (MPA) and L-Cysteine (Cys), and the resulting MPA@Sponge and Cys@Sponge showed significantly improved removal efficiency towards trace cisplatin and carboplatin against Sponge. MPA@Sponge achieved maximum removal of 88.9 ± 0.5% for cisplatin and 85.2 ± 0.4% for carboplatin, while Cys@Sponge achieved maximum removal of 75 ± 2% and 59 ± 1%. In contrast, Sponge only achieved removal of 29 ± 4% and 4 ± 1%, respectively. It suggests that thiol groups serve as favourable binding sites for Pt complexation. Carboplatin exhibits lower adsorption compared to cisplatin due to its limited hydration. However, the presence of Cl⁻ in stock and high temperature facilitate the hydration and the formation of active derivatives of carboplatin, thereby enhancing its adsorption. The rapid adsorption processes of cisplatin and carboplatin are well described by the pseudo-second-order kinetic model involving diffusion and chemisorption. The results from adsorption isotherms revealed a monolayer adsorption that aligns with the principles proposed by the Langmuir model. High temperature significantly enhances the adsorption, and the positive enthalpies indicate that the binding of Pt with thiol groups is endothermic process. X-ray absorption spectroscopy measurements at the Pt L₃-edge revealed a similar coordination environment of the adsorbed Pt on both functionalized adsorbents, which can be attributed to the formation of four Pt-S bonds during the adsorption. To assess the validity of the adsorption results under realistic medium conditions, an adsorption study was carried out by using diluted urine spiked with trace platinum cytostatic drugs to simulate hospital wastewater. 90.2 ± 0.3% of cisplatin and 77.0 ± 0.2% of carboplatin was effectively removed by MPA@Sponge from diluted urine.